Rotorua Geothermal Field: The role of science on thedevelopment and recovery of the geothermal system

Rob Reevesr.reeves@gns.cri.nz
20/11/2017

Brad Scottb.scott@gns.cri.nz

GNS ScienceOutline of talkContents•

Introducing the Rotorua
Geothermal Field(RGF)––Location
Geothermal features•

Timeline•

Key scientific summaries•

Moving forward•

Lessons
Photo: B Scott, GNS Science

GNS Science

The Rotorua Geothermal
OutlineField(RGF)of talk
• Heat from volcanic source (230k y caldera)• Geothermal surface area approx. 12 km2• Rotorua city built over the geothermalfield.
• Over 1500 geothermal surface features.
• Contains some of NZ’s last remaining
geysers.
• Strong IWI links to the geothermal activity.
• Relatively easy access to hot water throughshallow drill holes (e.g. 100°C water < 100mdeep).
• Geothermal resources used for:
•Cultural•
Tourism•
Heating (domestic and commercial)•
Pools (domestic and commercial)
Modified from Reeves et al., 2014

GNS ScienceExamples of surface geothermal features in theOutline
oftalk
RGF

From BOPRC (2012)

GNS ScienceRGF
timeline
Outlineof talkPre 1800
Maori usegeothermal
for cooking,bathing,heating

1970-1980
Surfacefeaturedeclineobserved

1944
50 wells
drilled1920’sFirst wells
drilled1985
500 wells
in use.
MoEScienceReport

1974
Summaryof RGF
science

1982
Monitoring ofthe RGF
commences

1992
Post boreclosure
scientificprogramme

1987
Boreclosure
programm
e begins

2005
Compilationof scientificmonitoring

1999
RGF
regional
planoperative

Photograph from Stewart (2017)

GNS Sciencest Scientific
1974
1
Outline of talksummary of Rotorua• Who:–1974 DSIR report - NZ Geological Survey, Geophysics
division DSIR, Chemistry Division DSIR

• Purpose:–Investigate the potential geothermal resources of theRotorua Geothermal Field• What:––Largely an exploratory report that included:• Geology - surface geology, bore geology, structuralassessments• Geophysics – resistivity, gravity, magnetic, heat flow,
ground temperature• Geochemistry – bores, springs
This report identified potential environmental issues withlarge-scale development at Rotorua

Report: DSIR (1974)
From DSIR (1974)

GNS ScienceFactors
Outlineeffectingof talk RGF
management 1970-1980••

Scientific–Changes in geyser activity• Pohutu Geyser eruptions smaller and shorter• Te Horu Geyser stopped–
Changes in hot spring behaviour• Water level decreases (overflows stop/decline)• Change of character (pH neutral to pH acidic)–
Estimated heat flow reduction at Whakarewarewa reduced by 30% between 1967 and 1984–
Estimated number of production bores 376–
No regulation of bore use
Social–Observations from large scale developments e.g. Loss of geyser valley, Wairakei associated with
the Wairakei Geothermal power Station in the 1950-60’s–Competing priorities developing between bore users vs tourist ventures vs conservationgroupsBut …lack of quantifiable data:–––

Observational data from scientists not up to public scrutiny.
Some patterns difficult to assess due to increasing urbanisation + altered water drainage patterns.
Poor understanding of natural variation vs exploration effect making interpretation difficult.

Therefore, intensive scientific data collection and monitoring programmes were established
1982-1985 via a taskforce and ultimately used as a basis for government intervention (MoE,1985).
GNS ScienceOutlineMoE,
1985of talk•

Who:–•

1985 Technical report - DSIR, Ministry of Works, Ministry of Energy, NZ Geological
Survey, University of Auckland

Purpose:A. To develop a model of the shallow sections of the Rotorua Geothermal System using
quantifiable data from which management plans can be developed.
B. Identify ways of reducing geothermal aquifer draw-off

•

What:
–––––––––––

Groundwater monitoring of multiple geothermal aquifers (water level, temperatures, chemistry)
Geothermal surface features (temperatures, flows, chemistry, descriptions)
Geothermal bore data (including location, use and reinjection, temperatures, chemistry)
Hydrology (groundwater, streams, structural, rainfall)
Geophysics (resistivity, heat flow, levelling, )Geology (bores)
Numerical model
Bore testing
Water energy use
Engineering design
Waste geothermal water disposal

Note that many of the science areas were able to compile limited historical data from previous work todemonstrate some time-series trends.
The taskforce report provided a clear link between the resource development and decline in surface
geothermal activity and aquifer levels
Report: Ministry of Energy (1985)
GNS ScienceExamplesdata in MoE (1985)
Outline ofoftalk
Surface feature data

Aquifer level data

pH and water temperature data from surface features

Descriptive data from 1967-69 (A) and 1984-85 (B)From Kissling (2014)

GNS ScienceGovernment(1987)
Outline of Intervention
talkMoE (1985) data confirmed that geothermal development had influenced surface
geothermal features + aquifer levels.
Measures introduced:–

Local city control over geothermal bores (>70°C, >61 m deep) was revoked–

All geothermal bores within 1.5km of Pohutu geyser closed and grouted–

Closure of all geothermal bores owned by a government department in Rotorua–

Promoting reinjection of geothermal fluids to moderate depths (>50m)–All bores to be licenced–

Royalty system for geothermal energy use introduced–RGF plan 1999

GNS ScienceImmediate post bore closure:
Outlineof talkscience
1985-1992•

Who – DSIR Geology and Geophysics/DSIR Chemistry•

Purpose–•Update geothermal science knowledge after the bore closures and update conceptual models of the Rotorua
system using monitoring and new data.

What–
–––
–

Geological history (units, ages, structure)
Geophysics• Resistivity to delineate geothermal field boundaries• Seismic reflection to investigate faulting and lakebed structure.
• Aerial thermal infrared• Gravity• Heat flow
Geochemistry• Cl fluxes to determine geothermal flow and heat flux
• Characterise hydrology (water/gas/isotopes)• Age dating• Soil gas flux
Drill holes to test geology, downhole conditions
Numerical models

Report: Geothermics (1992)
From Bradford (1992b)

Key points:––––

Multidisciplinary science using state-of the art techniques
Intensive studies
Collates monitoring data with 1-off surveys
Data from bores drilled as part of development provide critical scientific information

GNS ScienceImmediate post bore closure: Key science points
Outlineoftalk
1985-1992•••

Detailed conceptual models of the RGF developed
Numerical model improved
Summary of monitored changes
–––––

•

Pohutu, Kereru geysers - enhanced activity within 2 years of bore closures
Many hot springs in the northern part of the RGF show good recovery
Increase in flow and cl water from Kuirau Lake by 1988
Changes from sulphate water to chloride type water in features
Increase in heat flow, mass and chloride from Roto-a-Tamaheke

Overall – monitoring suggests large-scale field recovery (<4 years), although not all
surface features have recovered.

Cl flow from
Lake Roto-aTamaheke

GNS SciencePost bore closure: Science 1992 Outline of talk2005•Who – Bay of Plenty Regional Council•Purpose–•

Summarise science conducted by BOPRC since 2001 on the RGF with a focus
to inform the RGF management plan

What–––––

Surface feature monitoring at selected features
Chemistry (selected bores and surface features)
Soil gas survey
Fluid use (locations, quantities)
Numerical model updated•

Found 1992-2001 was the greatest period of feature recovery.

•Not all features recovered at the same rates. Some did not recover.

•The field is generally stable in terms of aquifer levels at current
extraction/reinjection rates.

Reports: BOPRC (2001, 2005), Scott and Cody (2000), Scott et al. (2005)

GNS ScienceRGF Water level data

Outline of talk75 m deep

64 m deep

Min level

157 m deep

Bore closures
Water levels from Kissling(2014)
GNS ScienceRGF
Currentstatus
Outlineof talk•

Regular monitoring–––•

Ad-hoc surveys––––––•

Water levels at dedicated monitor bores
Natural feature monitoring from “indicator” features
Reviews of the above data

Event response (e.g. anomalous geothermal activity)
Bore use (# bores + take)Numerical model updates
Aerial thermal infrared
Heat flow
Surface feature surveys

RGF Plan still in place (no update since 1999)

From Reeves et al (2014)

GNS ScienceMovingforward
Outlineof talk••Science–

RGF has recovered to a large extent from earlier development–

Data indicates that many water levels have stabilised in surface
features and monitor bores–

Some changes in surface thermal features are still occurring

Social and political–RGF plan up for review in 2018–

There is increasing pressure to use the geothermal resource fordevelopment–Can we use more, and if so, how much?

Can the science answer these questions considering lessons learnt?

GNS ScienceRGF Lessons - 1

Outline of talk•

The Rotorua Geothermal System largely recovered quickly from development
once large-scale action was taken.

•Quality, time series data that could provide baseline conditions were critical inestablishing trends.

•Establishing dedicated, long-term monitoring sites is needed for reliable, longterm data. This can be difficult in geothermal conditions.

•Complex hydrological models were developed from intensive scientific studies
that can provide management options.

•Research findings were maximised by using data (e.g. down hole temperatures)
obtained from developers and bore owners.

GNS ScienceRGF
Lessons-2
Outlineof talk•

Ongoing monitoring of surface thermal features and groundwater systems areneeded to quantify changes of the development regime.

•Be aware of the limitations of the science – e.g. small hydrological changes maybe
within the errors of computer models.

•It would have been good to have linked the science to regulatory frameworks
earlier e.g. mapping of geothermal surface features can be linked to environmental
or building regulations.

•Having expert teams easily communicating will assist with issue identification andsolving.

GNS ScienceReferences
Outline of talkBay of Plenty Regional Council, 2001. Rotorua Geothermal Field management monitoring. Environment BOP Environmental Report
2001/22. ISSN: 1172-5850
Bay of Plenty Regional Council, 2005. Rotorua Geothermal Field management monitoring Update:2005. Bay of Plenty Regional Council
Environmental Publication 2005/12. ISSN: 1175-9372.
Bay of Plenty Regional Council, 2012. Guideline for mapping and monitoring geothermal features. Guideline 2012/03. ISSN: 1179 9595.
Department of Scientific and Industrial research, 1974. Geothermal Resources Survey Rotorua Geothermal District 1974. D.S.I.R
Geothermal Report No. 6.
Geothermics, 1992. Special issue: Rotorua geothermal Field, New Zealand. Vol 21, No. 1/2.
Kissling, W. 2014. Rotorua Geothermal Bore Water level Assessment – 2014, GNS Science Consultancy Report 2014/199. 39 p.
Accessed from https://www.boprc.govt.nz/media/395573/rotorua-geothermal-bore-water-level-assessment-2014.pdf on 4/8/2017.
Ministry of Energy, 1985. The Rotorua geothermal Field. Technical Report of the Geothermal Monitoring Programme 1982-1985.
Ministry of Energy.
Reeves, R.R.; Scott, B.J.; Hall, J. 2014. 2014 Thermal infrared survey of the Rotorua and Lake Rotokawa-Mokoia Geothermal Fields,GNS Science Report 2014/57. 28 p
Scott, B.J., Cody, A. D., 2000. Response of the Rotorua geothermal system to exploitation and varying management regimes.
Geothermics 29 (4/5), pp 573-592.
Scott, B.J., Gordon, D. A., Cody, A. D., 2005. Recovery of Rotorua geothermal field, New Zealand: progress, issues and consequences.
Geothermics 34 (2), pp 159-183.
Stewart, C, 2017. 'Geothermal energy - Heat from the earth', Te Ara - the Encyclopedia of New Zealand,
http://www.TeAra.govt.nz/en/photograph/5419/maori-women-cooking-at-whakarewarewa (accessed 7 August 2017)

GNS Science